I have a big problem. I have Firmware 4.0 and didn´t install cios rev 8, os now I can´t start , ios downgrader, cios downgrader or wad manager. If i start cios rev 8 installer I´m getting an error und if I want to start cios or ios downgrader my wii restarts automaticly.
And .wad I can´t install because I have Firmware 4.0

I don't think your Wii's shipped with firmware 4.0...did it? If it didn't, reset the system memory and you'll probably go back down to version 3.4U (Assuming your in the US)..just make sure you backed up everything.

Go into the system options (from the Wii menu) and find Format Wii System Memory (Wii options, last selection on last page.) That will wipe all data from the Wii's internal memory, but it will wipe all your save games (backup what you can) and your channels...basically...everything is gone, your Mii's too.